1417

mother is usually an anxious mother and that part of hisjob is to allay this anxiety. Illness itself causes behaviourdisorders in children; guiding the mother in her handlingof these problems all adds up to good doctoring.

ACCIDENT PREVENTION

The student comes into homes that are often over-crowded and poor. The unguarded fire, the faulty plug,the drug cupboard within too easy reach of exploringfingers, the pot on the stove with a protruding handle-thestudent must almost subconsciously become aware ofthese risks and learn to warn mothers of their dangerswhen he goes into practice.

SOCIAL MEDICINE

The hospital social worker is an integral member of thehome-care team, and from her the student learns from thebeginning how to assess the patient’s needs and where tofind the appropriate help. He visits the local school forhandicapped children, training-centres, day-nurseries,and welfare centres. A realisation of how the under-

privileged live should make the doctor agitate for betterhousing. " I never realised human beings could live insuch squalor "-a remark from a potential social reformerof the future.Home care is one way of introducing the medical

undergraduate to family doctors and good family doctor-ing. He sees that there is no basic difference between thegood " hospital " doctor and the good " home doctor ",and that good medicine can be practised at home, thehospital being reserved for special problems.

CONCLUSION

A paediatric home-care unit offers many advantages inteaching the medical student how to deal with the commonillnesses of childhood. He learns that much illness canbe as satisfactorily dealt with in the home as in hospital.This sort of tuition prepares him for his future work in

practice.I should like to thank Dr. T. E. Oppe, director of the Pasdiatric

Unit, St. Mary’s Hospital, and the Sembal Trust for their grant tohome care.

Occasional Book

DEFECTIVE COLOUR-VISIONAN ambitious and successful book,! intended mainly for

geneticists and those engaged in anthropometric studies, aimsto define more clearly the problems of defective colour-visionand its relation to normal colour-vision. In the pathology ofcolour-vision defects, Dr. Kalmus believes that in protanopesthe red-responding cones are missing, while in deuteranopesprobably both red-responding and green-responding conescontain only the red-absorbing pigment. In tritanopes theblue-responding cones also are missing. As would be expectedfrom a geneticist of Dr. Kalmus’s standing, he deals admirablywith the complexities of the genetics of defective red-greencolour-vision. There is evidence that there are separate locifor the protan and deutan series, with two or three allelesbesides the normal dominant gene for each locus. But Dr.Kalmus seems still to favour the single-locus theory, althoughthe facts are very hard to fit into it.Of especial interest is Dr. Kalmus’s proposal to use the

anomaloscope to measure the matching range (whose importancewas emphasised by Franceschetti and by Willis and Farns-worth) as well as the matching point. In the first days of theanomaloscope it was assumed that the essential measurementwas the proportion of red to green light needed by theobserver to match the standard yellow, and it was understoodthat the yellow had to be varied in brightness, at least for somesubjects. But if we want an observer to match a standard

yellow in hue, saturation, and brightness with a mixture of redand green, then there are three dimensions of variability. Forevery subject we must measurer) the average proportions ofred to green which match the yellow for him, (b) the limits ofchange in these proportions before he notices a difference inhue and/or saturation, and (c) the variations in brightness ofeither the red-green mixture or the yellow standard betweenthese limits and, indeed, throughout the available range ofvariations. The yellow may have to be desaturated in step withthe other changes, but in practice this proves to be less impor-tant, and is seldom required. Few anomaloscopes provide fordesaturation of the yellow.A psychophysical technique in which the observer is asked

to change the controls for yellow brightness and red-greenmixture freely until he arrives at a match, even taking theaverage of several such readings, may work reasonably wellwith subjects who are practised at such adjustments and have1. Diagnosis and Genetics of Defective Colour Vision. By H. KALMUS,

M.D., SC.D. London: Pergamon Press. 1965. Pp. 114. 50s.

good colour discrimination; but the poorer the subject’s huediscrimination the less satisfactory the result. This techniqueis acceptable if the state of the subject’s colour discrimination isknown. An anomalous subject who has poor or very poorcolour discrimination but is not dichromatic may make five orsix settings, all different but equally good for him; but how arewe to know that his matching range has been properly measuredwhen a random technique is used ? We cannot even be surethat he is not a dichromat.

Dr. Kalmus has proposed to adapt the original technique bysetting the red-green mixture first at the fully red position andthen asking the subject to adjust the brightness of the yellow tomatch it. (Dichromats can do this, and so can certain extremeprotanomalous subjects whose matching range extends to thered end but not to the green end of the scale.) Then the subjectis given various brightnesses of yellow and asked to match themwith the red-green mixture, in order to find out whether he is adichromat or anomalous.

This kind of technique should be replaced by a systematicmeasurement of the subject’s matching range. The adjust-ments should be made by the tester, who must ask the subjectat each step whether there is a colour difference and what it is,no claim of an apparent colour difference being accepted untilthe halves of the test field are satisfactorily equated in brightnessfor the subject. The subject’s mid-point will be the middle ofhis matching range, and its deviation from the normal averagemid-point can be established, while his matching range andbrightness variation can be compared with those of othersubjects. Function fluctuation-manifested in the considerablevariability of results on repeated testing-is also important incertain anomalous subjects. For dichromats, of course, thematching range always extends from one end of the red-greenscale to the other (with appropriate brightness adjustments),and for them the mid-matching point is arbitrarily in the middleof the scale and is not comparable with that for other subjects.The same fundamental principle of aiming the test technique

primarily at measurement of matching range and its positioncan be used to identify dichromats; to distinguish protans fromdeutans; to determine the matching range and the deviation, ifany, of the mid-matching point for anomalous subjects; and todetermine the same variations found on a much smaller scale

among minor defectives (the deviants and colour-weak), whodo not, however, inherit a sex-linked abnormality. The sametechnique, using other spectral colours or other colour filters,according to the kind of anomaloscope employed, can be usedto measure variations of mid-matching point, matching range,and brightness level in other colour dimensions, such as

blue-to-green or yellow-to-blue.